As a thin plane light source used in liquid crystal displays, for example, there has been a surface mount light emitting device (hereinafter referred to as light emitting device), which is disposed on an edge surface of an optical waveguide provided on a bottom surface of a liquid crystal display unit.
In the plane light source, the optical waveguide and the light emitting device are provided so that the edge surface of the optical waveguide faces an emitting surface of the light emitting device.
Light emitted from the plane light source is incident on the edge surface of the optical waveguide, and emitted from a top plane surface of the optical waveguide.
For example, Japanese Unexamined Patent Publication 193537/2004 (Tokukai 2004-193537, publication date: Jul. 8, 2004) (Patent Document 1) discloses a light emitting device used in such a plane light source. The light emitting device disclosed in this publication includes a reflector for causing light to be efficiently incident on an edge surface of an optical waveguide.
The light emitting device includes a package body having a concave portion, which contains an LED chip (hereinafter referred to as chip) and in which a concave portion for extracting light to the outside is formed. The concave portion serves as a reflector formed in a flat shape and having an opening enlarged toward the edge surface of the optical waveguide.
The reflector (concave portion) has a bottom surface, on which a chip is mounted, and a side wall. The side wall is provided along an outer edge of the bottom surface so as to form an angle with the bottom surface. Further, the reflector is formed so that light is emitted in parallel to a mounting surface.
On the bottom surface of the concave portion, a die bonding region is provided in its substantially center part. Further, portions in the vicinity of both sides of the die bonding region are wire bonding regions, where electrodes for supplying an electric power are disposed in parallel.
The chip is mounted in the die bonding region, and connected to the electrodes with wires. Further, the concave portion is filled with a transparent sealing resin, a surface of which serves as the emitting surface.
Further, there have been light emitting devices that improve light extraction efficiency by suppressing a total reflection at a boundary between a sealing resin in a chip and air. One such light emitting device is described in, for example, Japanese Unexamined Patent Publication 516666/2004 (Tokuhyo 2004-516666), i.e., WO2002/050472 (international publication date: Jun. 27, 2002) (Patent Document 2).
The light emitting device described in this publication includes a chip; a polygon shape bottom surface on which the chip is mounted, a horn shape reflector, and a resin with which the chip is sealed. The reflector has a side wall provided with an angle along the outer edge of the bottom surface. The side wall of the reflector has a gentle slope surface and a steep slope surface, which are provided in this order from the bottom surface. Further, the reflector is filled with a sealing resin up to a level that sufficiently suppresses a total reflection from occurring at the boundary between a sealing resin and air.
However, the light emitting device described in Patent Document 1 merely includes a reflector having a single slope surface.
Further, the light emitting device described in Patent Document 2 includes a horn shape reflector, which has a polygon shape bottom surface including a gentle slope surface and a steep slope surface. Further, the reflector described in Patent Document 2 is filled with a resin up to a level that sufficiently suppresses the total reflection.
On the other hand, as a chip having a high intensity and high efficiency in light emission, there has been a known chip (element) that has emission characteristics of achieving a peak light intensity in a direction along a side of the chip. One such chip is, for example, an element which has a side surface inclined from its bottom surface to its top surface, and which includes an active layer in the vicinity of the bottom surface. However, in the reflector having the side surface described in Patent Document 1 and in the reflector having the gentle slope surface described in Patent Document 2, an active layer is provided in the vicinity of a bottom surface. Thus, in these reflectors, no consideration is mainly given to a situation where components of light emitted from a side surface of a chip can be reflected.
On the contrary, there has also been a chip that includes a light emitting section, i.e., active layer, provided at a position between the substantially center part of a chip and the vicinity of a top surface of the chip.
Further, in the reflector having the side surface described in Patent Document 1 and in the reflector having the gentle slope surface described in Patent Document 2, no consideration is given to a situation where a tilt angle is formed such that components of light emitted from a chip including an active layer between its substantially center part and the vicinity of its top surface is reflected efficiently.
Thus, in the light emitting devices described in these publications, light extraction efficiency has not been sufficient when such a chip is used.
Further, in the light emitting device described in Patent Document 1, the side wall of the reflector is merely made close to the vicinity of the chip. This narrows the area for the wire bonding region, causing difficulties in performing wire bonding.
Further, since the die bonding region is narrow, it has been difficult to mount a chip being large in size and emitting large mount of light.
Further, the light emitting device described in Patent Document 2 does not consider to provide a thin light emitting devices by forming the reflector in a compressed shape.